7 - Combined methods of drag reduction

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A brief description of eight combined drag reduction methods is given. The results of experimental studies of the hydrodynamic characteristics of rigid bodies with the xiphoid shape of the nasal parts are presented. Theoretical studies of the hydrodynamic characteristics of rigid bodies with the xiphoid shape of the nose are considered. A brief review of studies of the injection of polymer solutions into the boundary layer, and experimental equipment and research methods for the combined method of drag reduction are presented. The dependences of the drag coefficient on the Reynolds number of models with different nose shapes are obtained. The drag of a model with a lively tip was studied during injection of polymer solutions into the boundary layer. Photos of visualization of the boundary layer during the injection of water and polymer solutions are presented. The experimental results are presented for the drag of a model with xiphoid tips of various lengths and injection of polymer solutions into the boundary layer. The physical mechanism of the influence of the xiphoid tip on the drag reduction is considered. The results of a study are presented of the effect of a parietal jet injected from the nasal slit on the kinematic characteristics of the boundary layer of a longitudinally streamlined body in a stream flooded by a jet. The hydrodynamic features of the structure of the skin and body of swordfish are described. The hydrodynamic modeling of the considered features is carried out. In particular, experimental studies of the flow around deepening in water and air outflows have been performed. The patterns of visualization of the flow around the deepening’s are shown. A review of studies of the effect of injection into the boundary layer of microbubbles on the drag reduction is performed. The effect of bubble injection on drag reduction of an axisymmetric model is experimentally investigated. The hydrodynamic modeling of the development of disturbances in the flow behind the ledge is performed.